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Question about electrical motors and drives

Question about electrical motors and drives

Question about electrical motors and drives

(OP)
I am looking for an electrical motor that can pull a weight of about 250 kg vertically. I am also looking for some kind of driver that can controll the pulling power. The motor should beside beeing able to pull a certain load, also be able to work as a breaking mechanism when the load exceedes the weight the motor is set to pull. That means that if the motor is set to pull 200 kg and the load becomes higher, the motor should be able to give a resistance of 200 kg while beeing forced to rotate the wrong way. This is something the motor would have to do all the time. the whole device should weigh not much more than 10 kg. I was thinking about using an eddy current drive, but it became to big and heavy. I would really appreciate if anyone could give me some tips.

RE: Question about electrical motors and drives

One very important parameter that you didn't mention is how fast you need to lift the weight. Is it one meter in one minute? Or one meter in one second? The speed has a lot to do with what motor and drive you will need.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Question about electrical motors and drives

(OP)
Oh, sorry I forgot. The maximum speed is about 0.5 meters a second, maybee a little less

RE: Question about electrical motors and drives

No gearbox?

RE: Question about electrical motors and drives

(OP)
I was hoping to avoid it to keep it simple

RE: Question about electrical motors and drives

Keeping it simple will include a gear box...

Keith Cress
kcress - http://www.flaminsystems.com

RE: Question about electrical motors and drives

At the load you're looking for about 400 watts, a fairly small motor.  I doubt you find a motor that small that can handle a 250 kg radial load.  How low a speed do you want to go?  You may need a motor bigger than 400 watts if you need full torque at low speed.

RE: Question about electrical motors and drives

(OP)
Hi, and thanks for the replies so far. The motor would actually need to operate at a negative speed, where the load moves at minus 0,5 meters a second. in other words, the motor should be able act as a brake as well as a winch. I am considering a torque motor. Does anyone know if one of those would be able to do the job?  

RE: Question about electrical motors and drives

I looked at torque motors for a rotary table on a machine tool.  They are very expensive!  They're used where servo performance, small space, and no backlash are required.  As a servo motor, I believe you can command it to do almost anything including acting as a slip clutch (regen or dynamic braking).  You'd have to be able to command a load and keep it from overspeeding when you are allowing it to slip.  Some of the controls people here should be able to tell you if that's possible.

How do you intend to connect the load to the motor shaft?  Wrap the rope around the shaft?

RE: Question about electrical motors and drives

Hi Bob. The old torque motors were not sophisticated. Basically an induction motor designed to be able to be stalled indefinitely without overheating. They were also optimized for a flatter than normal torque curve. Just apply three phase power and the shaft tries to turn. It will if it can. But, much larger than a conventional motor of the same torque rating.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Question about electrical motors and drives

(OP)
Actually I was thinking of doing it as simple as possible in the line of wraping the rope around the shaft. Thats why I am considering a torque motor, so I can get high torque without using gears. I could of course also use a regular motor and a slip clutch, but I have not found a combination that would be light an small enough. I was looking at a hysteresis coupling, but the one I found had to be over 30 kilos to be able to give enough torque, and that is to heavy    

RE: Question about electrical motors and drives

Careful with wrapping the rope around the shaft.  If it's steel rope you can't have too small a bend radius or cable life will suffer.  For 250 kg, you'd probably need a minimum of 3 mm diameter wire rope (working load = rated load of cable/(safety factor of 4-5)).  Also, if you can't get the entire length of wrap on just one cable layer then you will need an external (to the motor) load sensor since the motor will try to control torque.

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